Inkjet printers employing Memjet® technology are commercially available for a number of different printing formats, including small-office-home-office (“SOHO”) printers, label printers and wideformat printers. Memjet® printers typically comprise one or more stationary inkjet printheads, which are user-replaceable. For example, a SOHO printer comprises a single user-replaceable multi-colored printhead, a high-speed label printer comprises a plurality of user-replaceable monochrome printheads aligned along a media feed direction, and a wideformat printer comprises a plurality of user-replaceable printheads in a staggered overlapping arrangement so as to span across a wideformat pagewidth.
Supplying ink to high-speed printheads can be problematic due to high ink flow requirements and the need to maintain supplied ink within a predetermined pressure range. Typically, inkjet printheads require ink to be supplied at a negative ink pressure (i.e. less than atmospheric pressure) and various ink delivery systems have been developed for providing a stable, negative ink pressure for a printhead.
In a gravity-feed ink delivery system, a pressure-regulating tank is positioned below the height of the printhead and has a gas port open to atmosphere. A level of ink in the tank is maintained relatively constant, for example, by controlling a supply of ink into the tank. A difference in height between the printhead and the head of ink in the pressure-regulating tank controls the backpressure in the printhead. Controlling the level of ink in the pressure-regulating tank may be achieved by any suitable means. For example, a float valve mechanism may be used to control the supply of ink into the tank, as described in U.S. Pat. No. 8,066,359, the contents of which are incorporated by reference. Alternatively, sensors may be used to detect the level of ink in the pressure-regulating tank and a valve and/or ink pump arrangement may be used to control the flow of ink into the tank via a suitable feedback and control system.
In other ink delivery systems, negative pressure is provided by connecting a gas port of the pressure-regulating tank to a pump. The pump is operable to provide a variable pressure in the headspace of the tank e.g. a constant negative headspace pressure for normal printing. In this way, the ink pressure is independent of the height of the tank thereby enabling more flexibility in the printer design.
A problem with the above-described ink delivery systems is that ink is necessarily exposed to air. However, some printheads perform optimally when supplied with degassed ink, which minimizes the risk of air bubbles affecting the performance of the printhead during long print runs. Exposure of degassed ink to air is problematic, because ink (especially turbulent ink) is readily regassed when in contact with air, thereby negating the benefits of using degassed ink. Accordingly, ink delivery systems which expose inks to air are not usually considered suitable for use with degassed inks.
It would be desirable to provide an ink delivery system and ink tank, which is suitable for use with degassed inks even when those inks are exposed to air for pressure regulation.